A standard utility grid comprises a number of power generators and consumers. The utility grid maintains a stable frequency value when power generated and consumed is in balance.
The frequency of the utility grid may rise if the consumed power suddenly drops and creates an unbalance between the power generated and consumed. Unfortunately when the frequency rises it may cause malfunction or even damage to any electrical equipment connected to it.
European patent application EP 1 467 463 A discloses a method for operating a wind farm where active power supplied to a grid is controlled in dependence of the grid frequency.
European patent EP 1 282 774 B discloses a method for operating a wind turbine during a power drop where the power delivered to the electrical network is regulated or adjusted in dependence on the network frequency of the electrical network.
A disadvantage of the mentioned prior art is that at a significant reduction of power, the wear and tear on the turbines may be critically high leading to early wear out of the turbine.
It is an object of the invention to provide technique without the above mentioned disadvantages and especially it is an object to provide technique which may be used in connection with any type of wind turbine.